Create a private Azure Kubernetes Service (AKS) cluster

This article helps you deploy a private link-based AKS cluster. If you're interested in creating an AKS cluster without required private link or tunnel, see Create an Azure Kubernetes Service cluster with API Server VNet Integration (Preview).

Overview

In a private cluster, the control plane or API server has internal IP addresses that are defined in the RFC1918 - Address Allocation for Private Internet document. By using a private cluster, you can ensure network traffic between your API server and your node pools remains only on the private network.

The control plane or API server is in an AKS-managed Azure resource group, and your cluster or node pool is in your resource group. The server and the cluster or node pool can communicate with each other through the Azure Private Link service in the API server virtual network and a private endpoint that's exposed on the subnet of your AKS cluster.

When you provision a private AKS cluster, AKS by default creates a private FQDN with a private DNS zone and an additional public FQDN with a corresponding A record in Azure public DNS. The agent nodes continue to use the A record in the private DNS zone to resolve the private IP address of the private endpoint for communication to the API server.

Region availability

Private cluster is available in public regions, Azure China cloud, and Azure operated by 21Vianet regions where AKS is supported.

Prerequisites

• The Azure CLI version 2.28.0 or higher. Run az --version to find the version, and run az upgrade to upgrade the version. If you need to install or upgrade, see Install Azure CLI.
• The aks-preview extension 0.5.29 or higher.
• If using Azure Resource Manager (ARM) or the Azure REST API, the AKS API version must be 2021-05-01 or higher.
• To use a custom DNS server, add the Azure public IP address 168.63.129.16 as the upstream DNS server in the custom DNS server, and make sure to add this public IP address as the first DNS server. For more information about the Azure IP address, see What is IP address 168.63.129.16?
  • The cluster's DNS zone should be what you forward to 168.63.129.16. You can find more information on zone names in Azure services DNS zone configuration.
• Existing AKS clusters enabled with API Server VNet Integration can have private cluster mode enabled. For more information, see Enable or disable private cluster mode on an existing cluster with API Server VNet Integration.

Limitations

• IP authorized ranges can't be applied to the private API server endpoint, they only apply to the public API server.
• Azure Private Link service limitations apply to private clusters.
• There's no support for Azure DevOps Microsoft-hosted Agents with private clusters. Consider using self-hosted agents.
• If you need to enable Azure Container Registry to work with a private AKS cluster, set up a private link for the container registry in the cluster virtual network or set up peering between the container registry's virtual network and the private cluster's virtual network.
• Deleting or modifying the private endpoint in the customer subnet will cause the cluster to stop functioning.

Create a private AKS cluster

Use custom domains

If you want to configure custom domains that can only be resolved internally, see Use custom domains.

Disable a public FQDN

Disable a public FQDN on a new cluster

• Disable a public FQDN when creating a private AKS cluster using the az aks create command with the --disable-public-fqdn flag.

  az aks create \
      --name <private-cluster-name> \
      --resource-group <private-cluster-resource-group> \
      --load-balancer-sku standard \
      --enable-private-cluster \
      --assign-identity <resourceID> \
      --private-dns-zone <private-dns-zone-mode> \
      --disable-public-fqdn \
      --generate-ssh-keys
  

Disable a public FQDN on an existing cluster

• Disable a public FQDN on an existing AKS cluster using the az aks update command with the --disable-public-fqdn flag.

  az aks update \
      --name <private-cluster-name> \
      --resource-group <private-cluster-resource-group> \
      --disable-public-fqdn
  

Configure a private DNS zone

You can configure private DNS zones using the following parameters:

• system: This is the default value. If the --private-dns-zone argument is omitted, AKS creates a private DNS zone in the node resource group.
• none: The default is public DNS. AKS won't create a private DNS zone.
• CUSTOM_PRIVATE_DNS_ZONE_RESOURCE_ID: This requires you to create a private DNS zone in the following format for Azure global cloud: privatelink.<region>.cx.prod.service.azk8s.cn or <subzone>.privatelink.<region>.cx.prod.service.azk8s.cn. You'll need the resource ID of the private DNS zone for future use. You also need a user-assigned identity or service principal with the Private DNS Zone Contributor and Network Contributor roles. When deploying using API server VNet integration, a private DNS zone supports the naming format of private.<region>.cx.prod.service.azk8s.cn or <subzone>.private.<region>.cx.prod.service.azk8s.cn. You can't change or delete this resource after creating the cluster, as it can cause performance issues and cluster upgrade failures.
  • If the private DNS zone is in a different subscription than the AKS cluster, you need to register the Microsoft.ContainerServices Azure provider in both subscriptions.
  • You can use fqdn-subdomain with CUSTOM_PRIVATE_DNS_ZONE_RESOURCE_ID only to provide subdomain capabilities to privatelink.<region>.cx.prod.service.azk8s.cn.
  • If your AKS cluster is configured with an Active Directory service principal, AKS doesn't support using a system-assigned managed identity with custom private DNS zone. The cluster must use user-assigned managed identity authentication.
  • If you're specifying a <subzone>, there's a 32 character limit for the <subzone> name.

properties.apiServerAccessProfile.privateDNSZone.
"apiServerAccessProfile": {
"enablePrivateCluster": true,
"privateDNSZone": "system|none|[resourceId(..., 'Microsoft.Network/privateDnsZones', 'privatelink.<region>.cx.prod.service.azk8s.cn']"
}

Create a private AKS cluster with a private DNS zone

• Create a private AKS cluster with a private DNS zone using the az aks create command with the following flags:

  az aks create \
      --name <private-cluster-name> \
      --resource-group <private-cluster-resource-group> \
      --load-balancer-sku standard \
      --enable-private-cluster \
      --assign-identity <resourceID> \
      --private-dns-zone [system|none] \
      --generate-ssh-keys
  

Create a private AKS cluster with a custom private DNS zone or private DNS subzone

• Create a private AKS cluster with a custom private DNS zone or subzone using the az aks create command with the following flags:

  # The custom private DNS zone name should be in the following format: "<subzone>.privatelink.<region>.cx.prod.service.azk8s.cn"
  
  az aks create \
      --name <private-cluster-name> \
      --resource-group <private-cluster-resource-group> \
      --load-balancer-sku standard \
      --enable-private-cluster \
      --assign-identity <resourceID> \
      --private-dns-zone <custom private dns zone or custom private dns subzone resourceID> \
      --generate-ssh-keys
  

Create a private AKS cluster with a custom private DNS zone and custom subdomain

• Create a private AKS cluster with a custom private DNS zone and subdomain using the az aks create command with the following flags:

  # The custom private DNS zone name should be in one of the following formats: "privatelink.<region>.cx.prod.service.azk8s.cn" or "<subzone>.privatelink.<region>.cx.prod.service.azk8s.cn"
  
  az aks create \
      --name <private-cluster-name> \
      --resource-group <private-cluster-resource-group> \
      --load-balancer-sku standard \
      --enable-private-cluster \
      --assign-identity <resourceID> \
      --private-dns-zone <custom private dns zone resourceID> \
      --fqdn-subdomain <subdomain> \
      --generate-ssh-keys
  

Update a private cluster from a private DNS zone to public

You can only update from byo or system to none. No other combination of update values is supported.

• Update a private cluster from byo or system to none using the az aks update command with the following flags:

  az aks update \
      --name <private-cluster-name> \
      --resource-group <private-cluster-resource-group> \
      --private-dns-zone none
  

Options for connecting to the private cluster

The API server endpoint has no public IP address. To manage the API server, you need to use a VM that has access to the AKS cluster's Azure Virtual Network (VNet). There are several options for establishing network connectivity to the private cluster:

• Create a VM in the same VNet as the AKS cluster using the az vm create command with the --vnet-name flag.
• Use a VM in a separate network and set up virtual network peering.
• Use an Express Route or VPN connection.
• Use the AKS command invoke feature.
• Use a private endpoint connection.

Creating a VM in the same VNet as the AKS cluster is the easiest option. Express Route and VPNs add costs and require additional networking complexity. Virtual network peering requires you to plan your network CIDR ranges to ensure there are no overlapping ranges.

Virtual network peering

To use virtual network peering, you need to set up a link between the virtual network and the private DNS zone.

Hub and spoke with custom DNS

Hub and spoke architectures are commonly used to deploy networks in Azure. In many of these deployments, DNS settings in the spoke VNets are configured to reference a central DNS forwarder to allow for on-premises and Azure-based DNS resolution.

When deploying an AKS cluster into such a networking environment, there are some special considerations:

• When a private cluster is provisioned, a private endpoint (1) and a private DNS zone (2) are created in the cluster-managed resource group by default. The cluster uses an A record in the private zone to resolve the IP of the private endpoint for communication to the API server.
• The private DNS zone is linked only to the VNet that the cluster nodes are attached to (3). This means that the private endpoint can only be resolved by hosts in that linked VNet. In scenarios where no custom DNS is configured on the VNet (default), this works without issue as hosts point at 168.63.129.16 for DNS that can resolve records in the private DNS zone because of the link.
• In scenarios where the VNet containing your cluster has custom DNS settings (4), cluster deployment fails unless the private DNS zone is linked to the VNet that contains the custom DNS resolvers (5). This link can be created manually after the private zone is created during cluster provisioning or via automation upon detection of creation of the zone using event-based deployment mechanisms (for example, Azure Event Grid and Azure Functions). To avoid cluster failure during initial deployment, the cluster can be deployed with the private DNS zone resource ID. This only works with resource type Microsoft.ContainerService/managedCluster and API version 2022-07-01. Using an older version with an ARM template or Bicep resource definition isn't supported.

Use a private endpoint connection

A private endpoint can be set up so that a VNet doesn't need to be peered to communicate with the private cluster. Create a new private endpoint in the virtual network containing the consuming resources, and then create a link between your virtual network and a new private DNS zone in the same network.

Create a private endpoint resource

Create a private endpoint resource in your VNet:

1. From the Azure portal home page, select Create a resource.
2. Search for Private Endpoint and select Create > Private Endpoint.
3. Select Create.
4. On the Basics tab, configure the following settings:
   • Project details
     • Subscription: Select the subscription where your private cluster is located.
     • Resource group: Select the resource group that contains your virtual network.
   • Instance details
     • Name: Enter a name for your private endpoint, such as myPrivateEndpoint.
     • Region: Select the same region as your virtual network.
5. Select Next: Resource and configure the following settings:
   • Connection method: Select Connect to an Azure resource in my directory.
   • Subscription: Select the subscription where your private cluster is located.
   • Resource type: Select Microsoft.ContainerService/managedClusters.
   • Resource: Select your private cluster.
   • Target sub-resource: Select management.
6. Select Next: Virtual Network and configure the following settings:
   • Networking
     • Virtual network: Select your virtual network.
     • Subnet: Select your subnet.
7. Select Next: DNS > Next: Tags and (optionally) set up key-values as needed.
8. Select Next: Review + create > Create.

Once the resource is created, record the private IP address of the private endpoint for future use.

Create a private DNS zone

Once you create the private endpoint, create a new private DNS zone with the same name as the private DNS zone created by the private cluster. Remember to create this DNS zone in the VNet containing the consuming resources.

1. In the Azure portal, navigate to your node resource group and select your private DNS zone resource.
2. In the service menu, under DNS Management, select Recordsets and note the following:
   • The name of the private DNS zone, which follows the pattern *.privatelink.<region>.cx.prod.service.azk8s.cn.
   • The name of the A record (excluding the private DNS name).
   • The time-to-live (TTL).
3. From the Azure portal home page, select Create a resource.
4. Search for Private DNS zone and select Create > Private DNS zone.
5. On the Basics tab, configure the following settings:
   • Project details:
     • Select your Subscription.
     • Select the Resource group where you created the private endpoint.
   • Instance details
     • Name: Enter the name of the DNS zone retrieved from previous steps.
     • Region defaults to the location of your resource group.
6. Select Review + create > Create.

Create an A record

Once the private DNS zone is created, create an A record, which associates the private endpoint to the private cluster:

1. Go to the private DNS zone you created in previous steps.
2. In the service menu, under DNS Management, select Recordsets > Add.
3. On the Add record set page, configure the following settings:
   • Name: Enter the name retrieved from the A record in the private cluster's DNS zone.
   • Type: Select A - Address record.
   • TTL: Enter the number from the A record in the private cluster's DNS zone.
   • TTL unit: Change the dropdown value to match the one in the A record from the private cluster's DNS zone.
   • IP address: Enter the IP address of the private endpoint you created.
4. Select Add to create the A record.

Link the private DNS zone to the virtual network

Once the A record is created, link the private DNS zone to the virtual network that will access the private cluster:

1. Go to the private DNS zone you created in previous steps.
2. In the service menu, under DNS Management, select Virtual Network Links > Add.
3. On the Add Virtual Network Link page, configure the following settings:
   • Link name: Enter a name for your virtual network link.
   • Subscription: Select the subscription where your private cluster is located.
   • Virtual Network: Select the virtual network of your private cluster.
4. Select Create to create the link.

It might take a few minutes for the operation to complete. Once the virtual network link is created, you can access it from the Virtual Network Links tab you used in step 2.

Next steps

For associated best practices, see Best practices for network connectivity and security in AKS.